Toolholder

ABSTRACT

A toolholder ( 50 ) with a controllable critical angle, such as a lead, trailing, rake or clearance angles, includes a tool spindle ( 42   a ) for retaining the toolholder in a tool rest ( 42 ) of a machine tool. The machine tool ( 10 ) includes at least one linear axis, for example, three mutually perpendicular axes, a rotary axis and a rotation axis. The rotary axis and/or rotation axis is controllable to move to a specified position in synchronization with a movement of one of the linear axes. An adaptor ( 54 ) supports a cutting tool ( 56 ) that is retained in the adaptor by a clamp ( 58 ). The cutting tool ( 56 ) defines a critical angle, such as a lead angle, a trailing angle, a rake angle and a flank clearance angle, wherein the critical angle is corrected as a vector of movement of at least one of the linear axis is changed. In addition, the cutting tool ( 56 ) can be positioned on opposite side of a centerline of rotation of the workpiece to effectively double the life of the cutting tool. A method of controlling a toolholder ( 50 ) is also disclosed.

RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/407,864, filed on Sep. 3, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a toolholder with selectable critical angles,such as a lead angle, a trailing angle, a rake angle, and a flankclearance angle. More particularly, this invention relates to machinetool for turning and threading operations, such as a lathe or amachining center, that allows a specified relationship between theinsert geometry and the workpiece to be selectively determined by asoftware program of a numerically controlled machine tool to maintain acritical angle between the insert and the workpiece as the geometry ofthe workpiece changes.

2. Description of the Related Art

In most advanced machine tools, movement and control of the machine andits components are actuated by computer numerical controls (CNC). Thesemachine tools are usually equipped with one or more turrets. Each turretcan be equipped with a variety of tools and performs several operationson different surfaces of the workpiece.

Typically, a turning operation is performed in two linear axes, such asthe X- and Z-axes. A third linear axis, such as the Y-axis, can be addedto a turning machine tool to support milling operations in that axis,but not turning operations. As a result, a dedicated toolholder has beenrequired for each desired unique lead angle, thereby increasing thecosts associated with the machining operation.

In addition, the rake face of the cutting insert in conventionalthreading tools is in the X- and Z-axes. As pitch angles increase, theangle between the rake face and the thread becomes significant.Likewise, the clearance angles must be changed, in particular on theleading edge where the angle of the thread may exceed the typicalclearance angles, resulting in interference. Therefore, cutting insertsare frequently ground specifically for threads of a specific pitchangle. Manufacturers of such products with various pitch angles musttherefore purchase and inventory cutting inserts specifically for eachpitch angle.

SUMMARY OF THE INVENTION

Briefly, according to this invention, there is provided a machine toolcomprising at least three axes of linear motion, and at least a rotationaxis, the at least one rotation axis being controllable to move to aspecified position in sequential or simultaneous synchronization with amovement of one of the at least three axes of linear motion, and atoolholder mounted to a tool rest, the toolholder including a cuttingtool defining a critical angle with respect to a workpiece, wherein thecritical angle is corrected as a vector of movement of at least one ofthe linear axes is changed.

In another aspect of the invention, a machine tool comprising at leastthree axes of linear motion, and one of a rotary axis and a rotationaxis, the one of the rotary axis and rotation axis being controllable tomove to a specified position in synchronization with a movement of oneof the at least three axes of linear motion, and a toolholder mounted toa tool rest, the toolholder including a cutting tool defining a leadangle with respect to a workpiece, wherein the lead angle is selectivelydetermined by controlling the rotary axis to move to a specified portionof the workpiece at a specified velocity in synchronization with amovement of one of the at least three axes of linear motion.

In yet another aspect of the invention, a controllable toolholder, thetoolholder being mounted in a tool rest of a machine tool comprising atleast three axes of linear motion, and at least a rotation axis, the atleast one rotation axis being controllable to move to a specifiedposition in synchronization with a movement of one of the at least threeaxes of linear motion. The toolholder comprises a tool spindle forretaining the toolholder in a tool rest, an adaptor for supporting acutting tool retained in the adaptor by a clamp, the cutting tooldefining a critical angle, wherein the critical angle is corrected as avector of movement of at least one of the linear axis is changed.

In still yet another aspect of the invention, a method of controlling amachine tool, the machine tool comprising at least three axes of linearmotion, one of a rotary axis and a rotation axis, and a toolholdermounted to a tool rest, the toolholder including a cutting tool defininga critical angle with respect to a workpiece, the method comprises thesteps of:

moving one of the rotary axis and rotation axis to a specified positionin synchronization with a movement of one of the at least three axes oflinear motion,

correcting the critical angle as a vector of movement of at least one ofthe linear axis is changed.

In yet another aspect of the invention, a method of controlling atoolholder with a cutting tool, comprises the steps of:

reversing a direction of rotation of a workpiece, and

positioning the cutting tool on opposite side of a centerline ofrotation of the workpiece.

In still yet another aspect of the invention, a method of controlling amachine tool comprising at least three axes of linear motion, one of arotary axis and a rotation axis, and a toolholder mounted to a toolrest, the toolholder including a cutting tool, the method comprising thesteps of providing a macro including a geometry of a workpiece to bemachined and a geometric relationship of the cutting tool with respectto the workpiece, whereby the macro calculates the required movements ofthe at least three axes of linear motion, and one of the rotary axis androtation axis required to maintain a specified cutting tool geometry asthe cutting tool proceeds across a surface of the workpiece.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features of the present invention, as well as the advantagesderived therefrom, will become clear from the following detaileddescription made with reference to the drawings in which:

FIG. 1 shows a control block diagram of a machine tool with a toolholderof the invention;

FIG. 2 shows a perspective view of the toolholder according to theinvention;

FIG. 3 shows a side view of the toolholder of FIG. 2;

FIG. 4 shows a top view of the toolholder of FIG. 2;

FIG. 5(a)-(c) show a top view of the toolholder engaging the workpiecewith controllable lead and/or tling angles in accordance with theinvention; and

FIGS. 6(a) and (b) show a perspective view of the cutting tool, such asa wiper insert, engaging the workpiece with a relatively large trailingangle on roughing passes and a minimum trailing angle on the finishingpass, respectively.

FIG. 7 shows a machine tool with a toolholder for optimizing the rakeangle of the cutting tool as the cutting tool travels around theworkpiece;

FIG. 8 shows another embodiment of a machine tool with a toolholder foroptimizing the rake angle of the cutting tool as the cutting tooltravels around the workpiece;

FIGS. 9(a) and (b) shows one aspect of the invention in which themachine tool and toolholder can be moved along the Y-axis and positionedon either side of the longitudinal axis of the workpiece; and

FIG. 10 shows a side view of the toolholder of FIG. 2 with an offsetbetween the centerline of the workpiece and the toolholder rake face.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, wherein like reference characters representlike elements, FIG. 1 illustrates a machine tool 10 that is actuated bycomputer numerical controls (CNC). The machine tool 10 has a maincontrol portion 12, an input portion 14, such as a keyboard, a systemprogram memory 16, a tool file 18, a machining program memory 20, aspindle control portion 22, a tool rest control portion 24, and adisplay 26 that are connected through a bus line 28. A spindle motor 30is connected with the spindle control portion 22. The spindle motor 30rotates a spindle 32 with an axial center CT that is parallel to adirection of the Z-axis. The machine tool 10 also includes a chuck 34with chuck jaws 36 for holding and releasing a workpiece 38 having anouter diameter, D1. The spindle control portion 22 is capable of movingthe workpiece 38 in the X-axis direction, as indicated by arrows C andD. When the workpiece 38 is installed in the chuck jaws 36, alongitudinal axis, LW, of the workpiece 38 corresponds to the rotationaxis axial center CT of the spindle 32.

The machine tool 10 includes one or more tool rest driving motors 40that are connected to the tool rest control portion 24. A tool rest 42is connected to the tool rest driving motor 40 and is capable ofmovement in the Z-axis direction and in the X-axis direction, asindicated by the arrows E and F. In addition, the tool rest 42 iscapable of movement in a Y-axis direction (into and out of the paper),and in a B-axis direction, as indicated by the arrows G and H, by thetool rest driving motor 40. An example of a machine tool actuated by CNCis described in EP 1 186 367 A1, the entire contents of which isincorporated herein by reference.

A tool spindle 42 a is formed on the tool rest 42. A toolholder, showngenerally at 50 according to the present invention, can be attached,detached and exchanged with the tool spindle 42 a. The tool spindle 42 acan be of a quick change type as described in U.S. Pat. No. 6,415,696,the entire contents of which is incorporated herein by reference. Thetool spindle 42 a is free to fix and hold the toolholder 50 and othertools in a predetermined holding state, and is free to rotate, drive andposition around a rotation axis (axial center) CT2. Thus, the machinetool 10 includes a rotary axis (B-axis), a rotation axis, CT2, and threeaxes of linear motion (X-axis, Y-axis and Z-axis). When the toolholder50 is installed in the tool rest 42, a longitudinal axis, L, orcenterline of the toolholder 50 corresponds to the rotation axis CT2 ofthe tool rest 42.

Referring now to FIGS. 2-4, the toolholder 50 includes a tool shank 52for retaining the toolholder 50 in the tool rest 42 (FIG. 1). Thetoolholder 50 also includes an adaptor 54 for supporting a cutting tool56 attached to or securely fixed in a stationary position to the adaptor54 by a means well known in the art, such as a clamp 58. As best seen inFIG. 3, a rake angle 61 is defined as the angle formed between the topof the cutting tool 56 (rake face 57) and the plane passing through thelongitudinal axis, LW, or centerline of the workpiece 38. A flankclearance angle 63 is defined as the angle formed between the cuttingedge of the cutting tool 56 and the workpiece 38, sometimes referred toas an end relief angle. As best seen in FIG. 4, a lead angle 60 isdefined as the angle formed between the leading edge of the cutting tool56 and the workpiece 38. In addition, a trailing angle 62 is defined asthe angle formed between the trailing edge of the cutting tool 56 andthe workpiece 38. Preferably, the cutting tool 56 includes a cuttingtool nose radius 64 that is substantially concentric with thelongitudinal axis, L, or centerline of the toolholder 50 to eliminateprojection errors when re-orientating the lead angle 60 of the cuttingtool 56. However, the invention can be practiced without the cuttingtool nose radius 64 being substantially concentric with the longitudinalaxis, L, or centerline of the toolholder 50.

An aspect of the toolholder 50 of the invention is that a criticalangle, such as the lead angle 60 and/or the trailing angle 62, of thecutting tool 56 is selectively determined by the software program of theCNC for each portion of the geometry of the workpiece 38 as a vector ofmovement of one of the linear axes is changed. The lead angle 60 and/orthe trailing angle 62 can be selectively determined by controlling therotary axis (B-axis) and/or rotation axis, CT2, of the machine tool 10to move to a specified position in synchronization with the movement ofone of the three axes of linear motion (X-axis, Y-axis and Z-axis). Inaddition, the machine tool 10 can be programmed to move at a specifiedvelocity in sequential or simultaneous synchronization with the movementof one of the three axes of linear motion (X-axis, Y-axis and Z-axis).

Specifically, the critical angle, such as the lead angle 60 and/or thetrailing angle 62, can be selectively determined by controlling therotary axis, B, and/or the rotation axis CT2 independently of the linearaxis (X-axis, Y-axis and Z-axis). When the linear axes (X-axis, Y-axisand Z-axis) are programmed independently of the rotary and rotation axes(B and CT2), the velocity is typically expressed in units of inches ormm per min. However, most controls do not allow the units to be mixed,so simultaneous linear and rotary moves are frequently specified in“inverse time”. In this case, the time allowed for repositioning of thevarious axes is specified, and the control system back calculates thevelocity required for each axis to reach the destination coordinates atthe specified point in time.

Specifically, the machine tool 10 can be programmed with a macro that isprovided to the programmer into which the programmer specifies thegeometry of the part to be machined and the geometric relationship ofthe cutting tool 56 to the workpiece 38. The macro calculates therequired movements of the linear and rotary axis required to maintainthe specified cutting tool geometry as the cutting tool 56 proceedsacross the surface of the workpiece 38. Alternatively, the programmercan manually specify the velocity of traverse of the cutting tool 56across the workpiece 38 and the macro can calculate the requiredvelocity for each axis.

Referring now to FIG. 5, a lead angle 60 is dynamically re-orientatedrelative to the geometry of the workpiece 38 as the cutting tool 56moves relative to the workpiece 38, as shown in views (a), (b) and (c).Specifically, the lead angle 60 of the cutting tool 56 (as viewed in theplane of interpolation relative to a specific reference axis or initialconditions) can be specified in the program software, and the CNC cancalculate and command rotation of the cutting tool 56 about the rotaryaxis (B-axis) and/or the rotation axis CT2 such that the lead angle 60of the cutting tool 56 is adjusted and can be sequentially orcontinuously repositioned with respect to the geometry of the workpiece38 to maintain a specified value as the vector of movement of at leastone of the linear axes (X-axis, Y-axis or Z-axis) is changed.

In addition, the lead angle 60 can be used to anticipate interferencebetween the cutting tool 56 and geometrical features of the workpiece38. For example, the program software can react to an anticipatedinterference in several ways. One way is to generate an alarm to notifythe operator of the anticipated interference. Another way is toautomatically override the specified clearance angle 60 to prevent theanticipated interference without the need for operator intervention.

Likewise, the trailing angle 62 can be specified in the programsoftware, and the CNC can calculate and command rotation of the cuttingtool 56 about the rotary axis (B-axis) and/or the rotation axis CT2 suchthat the trailing angle 62 is corrected and can be sequentially orcontinuously repositioned with respect to the geometry of the workpiece38 to maintain a specified value as the vector of movement of at leastone of the linear axes (X-axis, Y-axis or Z-axis) is changed. Bydynamically repositioning the lead angle 60 and/or the trailing angle 62relative to the geometry of the workpiece 38, the performance of thecutting tool 56 is optimized, particularly when the cutting tool 56comprises a wiper insert in a turning operation.

Referring now to FIG. 6, the trailing angle 62 of the wiper cutting tool56 can be selectively orientated with respect to the workpiece 38 suchthat the wiper does not contact the workpiece 38 during roughing passes,and only contacts the workpiece 38 during the finish pass, therebyextending the life of the wiper cutting tool 56, as shown in views (a)and (b). By selectively optimizing the trailing angle 62 for eachportion of the geometry of the workpiece 38, a superior surface finishon the surface of the workpiece 28 having a complex geometry isachieved. In addition, the life of the cutting tool 56 can be optimizedby allowing the trailing angle 62 to be reduced to an optimum value forfinishing only when finishing is being performed, thereby protectingthat portion of the cutting tool 56 that is used during other cuttingoperations. Further, by selectively controlling the trailing angle 62 tobe an optimized value, a superior surface finish at high feed ratesnormally obtained only with wiper inserts can be achieve withconventional inserts, thereby reducing tool inventories and setupcomplexity. Alternatively, improved surface finishes can be obtainedwith conventional wiper inserts by selectively controlling the trailingangle 62 to an optimized value such that the wiper portion of the insertremains substantially tangent to the workpiece 28.

However, there are a variety of special turning operations, such assteep pitch angle turning (grooving and threading), in which toolperformance is not optimized with the traditional orientation of thecutting insert with the rake face in the X-Y plane. The presentinvention provides a method and device to orient the cutting tool thatoptimizes tool performance by orienting the rake face 57 (FIG. 3) normalto the path of the cutting tool 56 as it travels around the workpiece38.

In general, the present invention utilizes the rotary axis, B, and/orthe rotation axis, CT2, so that the cutting tool 56 can be positionednormal to a pitch angle 65 of the thread to be machined. When the rotaryaxis, B, and/or rotation axis, CT2, is in a reference position, and ifthe rake angle 61 is essentially zero, then the rake face 57 isessentially in the X-Z plane and the clearance angles (on both sides ofthe cutting tool 56) are essentially symmetrical. Before initiation ofthe threading cycle, the rotary axis, B, and/or rotation axis, CT2, isrotated to bring the rake face 57 perpendicular to the pitch of thethread. Then, the threading cycle to be performed in the X- and Z-axisis initiated.

One technique for optimizing the orientation of the rake angle 61 as thecutting tool 56 travels around the workpiece 38 is shown in FIG. 7. Thefirst technique positions the rake face 57 of the cutting tool 56 normalor perpendicular to a pitch angle 65 as the cutting tool 56 travelsalong the Z-axis to form the thread in the workpiece 38. This isaccomplished by rotating the rotation axis, CT2, of the machine tool 10to be substantially equal to the pitch angle 65 so as to position therake face 57 of the cutting tool 56 normal to the pitch angle 65. Inthis technique, the depth of cut is determined by the tool holder 50 asit travels along the X-axis. Thus, this technique uses a tool machineconfiguration in which the workpiece 38 is rotated (as indicated by thearrow), two axes of linear motion (X- and Z-axis) for positioning of thecutting tool 56, and the rotation axis, CT2, for positioning of thecutting tool 56, where the rotation axis, CT2, has a centerline in theX-Z plane and parallel to the X-axis. It will be appreciated that thepitch angle 65 can be selected as a function of the geometry of theworkpiece 38 and the cutting tool 56 to obtain a desired clearance angledefined as the angle between the flank face of the cutting tool 56 andthe workpiece 38.

Another technique for optimizing the orientation of the rake angle 61 isshown in FIG. 8. This technique also positions the rake face 57 of thecutting tool 56 normal or perpendicular to the pitch angle 65 as thetoolholder 50 travels along the Z-axis to form the thread in theworkpiece 38. This is accomplished by rotating the rotary axis, B, ofthe machine tool 10 to be substantially equal to the pitch angle 65 soas to position the rake face 57 of the cutting tool 56 normal to thepitch angle 65. In this technique, the depth of cut is determined by thetoolholder 50 as it travels along the Y-axis (into the page).

Another aspect of the invention is that the cutting tool 56 can bepositioned on either side of the longitudinal axis, LW, or centerline ofthe workpiece 38, as shown in FIG. 9. In FIG. 9(a), the cutting tool 56is positioned on one side (below) the centerline LW of the workpiece 38.In this position, a flank 56 a of the cutting tool 56 is being utilizedto perform the machine operation as the workpiece 38 rotates in a firstdirection. By utilizing the Y-axis on each side of the longitudinalaxis, LW, or centerline of the workpiece 38, as shown in FIG. 9(b), aflank 56 b of the cutting tool 56 is being utilized to perform themachine operation while the workpiece 38 rotates in a second, oppositedirection. By reversing a direction of rotation of a workpiece, andpositioning the cutting tool on opposite side of a centerline ofrotation of the workpiece, the number of flank faces applied to themachining process is doubled, effectively doubling tool life. Using thisaspect of the invention is highly desirable when the mode of ultimatetool failure is at DOC (depth of cut), particularly when machiningstainless and high-temperature alloys in which the most severe tool wearis at the point on the flanks 56 a, 56 b of the cutting tool 56.

Yet another aspect of the invention is that the rake face 57 of thecutting tool 56 can be positioned on either side of the longitudinalaxis, LX, of the workpiece 38 by a distance, H, as shown in FIG. 10. Itis noted that the longitudinal axis, LX, is substantially perpendicularto the Y-axis and substantially parallel to the X-axis. Noting that thedistance, H, is directly proportional to the diameter of the workpiece38, the cutting tool 50 can be programmed to vary the distance, H, asthe cutting tool 50 removes material and moves towards the center of theworkpiece 38. Thus, the clearance angle 63 can be programmed to remainconstant as the cutting tool 50 moves towards the center of theworkpiece 38. It will be appreciated that the distance, H, can be variedalong the Y-axis, as well as the X-axis, depending on the orientation ofthe rake face 57 of the cutting tool 56.

As described above, the present invention provides a controllabletoolholder for a machine tool having movement along at least one linearaxis, and having at least one rotary and/or rotation axis. It should beappreciated that the embodiments described above are representative ofonly a few of the possible machine tool configurations in which theprinciples of the invention can be applied, and that the principles ofthe invention can be applied to any machine tool configuration with theappropriate range of movements.

The documents, patents and patent applications referred to herein arehereby incorporated by reference.

While the invention has been specifically described in connection withvarious embodiments thereof, it is to be understood that this is by wayof illustration and not of limitation, and the scope of the appendedclaims should be construed as broadly as the prior art will permit.

1. A machine tool comprising at least one linear axis, and one of arotary axis and a rotation axis, one of the rotary axis and rotationaxis being programmable to move to a specified position in sequential orsimultaneous synchronization with a movement of the at least one linearaxis, and a toolholder mounted to a tool rest, the toolholder includinga cutting tool defining a lead angle or a trailing angle with respect tothe workpiece, wherein the lead angle or the trailing angle remainsconstant by controlling the movement of one of the rotary axis androtation axis about an axis other than a centerline of the workpieceindependently of the movement of the at least one linear axis.
 2. Themachine tool according to claim 1, wherein the cutting tool defines afirst trailing angle during a roughing pass and a second trailing angleduring a finishing pass, the second trailing angle being different thanthe first trailing angle.
 3. The machine tool according to claim 1,wherein the cutting tool includes a cutting tool nose radius that issubstantially concentric with a longitudinal axis of the toolholder. 4.The machine tool according to claim 1, wherein the cutting tool ispositioned on one side of the centerline of the workpiece when theworkpiece rotates in a first direction, and wherein the cutting tool ispositioned on an opposite side of the centerline of the workpiece whenthe workpiece rotates in a second, opposite direction.
 5. The machinetool according to claim 1, wherein the lead angle of the cutting tool isused to anticipate interference between the cutting tool and theworkpiece.
 6. The machine tool according to claim 1, wherein a clearanceangle of the cutting tool is adjusted with respect to a geometry of theworkpiece.
 7. The machine tool according to claim 1, wherein the leadangle of the cutting tool is adjusted with respect to a geometry of theworkpiece.
 8. The machine tool according to claim 1, wherein a rake faceof the cutting tool is substantially perpendicular to a longitudinalaxis of the toolholder.
 9. A machine tool comprising at least threemutually perpendicular linear axes, and one of a rotary axis and arotation axis, the one of the rotary axis and rotation axis beingprogrammable to move to a specified position in synchronization with amovement of one of the at least three mutually perpendicular linearaxes, and a toolholder mounted to a tool rest, the toolholder includinga cutting tool defining a lead angle with respect to a workpiece,wherein the lead angle is selectively determined by programming therotary axis to move about an axis other than a longitudinal axis of theworkpiece to a specific portion of the workpiece at a specific velocityin synchronization with a movement of one of the at least three mutuallyperpendicular linear axes.
 10. The machine tool according to claim 9,the machine tool back calculates the specific velocity for each linearaxis to intersect the specific portion of the workpiece at a specificpoint in time.
 11. A programmable toolholder, the toolholder beingmounted in a tool rest of a machine tool comprising at least threemutually perpendicular linear axes, and one of a rotary axis and arotation axis, the one of the rotary axis and rotation axis beingprogrammable to move to a specific position in synchronization with amovement of one of the at least three mutually perpendicular linearaxes, the toolholder comprising: a tool spindle for retaining thetoolholder in a tool rest; an adaptor for supporting a cutting tool,said cutting tool being retained in the adaptor by a clamp, the cuttingtool defining a lead angle or a trailing angle, wherein the lead angleor the trailing angle reins constant by moving one of the rotary axisand rotation axis about an axis other than a centerline of the workpieceindependently of the movement of the at least three mutuallyperpendicular linear axes.
 12. The toolholder according to claim 11,wherein the cutting tool defines a first trailing angle during aroughing pass and a second trailing angle during a finishing pass, thesecond trailing angle being different than the first trailing angle. 13.The toolholder according to claim 11, wherein the cutting tool includesa cutting tool nose radius that is substantially concentric with alongitudinal axis of the toolholder.
 14. The toolholder according toclaim 11, wherein the cutting tool is positioned on one side of acenterline of the workpiece when the workpiece rotate in a fistdirection, and wherein the cutting tool is positioned on an oppositeside of the centerline of the workpiece when the workpiece rotates in asecond, opposite direction.
 15. A method of programming a machine tool,the machine tool comprising at least three mutually perpendicular linearaxes, one of a rotary axis and a rotation axis, and a toolholder mountedto a tool rest, the toolholder including a cutting tool defining a leadangle or a trailing angle with respect to a workpiece, the methodcomprising the steps of: independently moving one of the rotary axis androtation axis about an axis other than a centerline of the workpiece toa specified position in synchronization with a movement of one of the atleast three mutually perpendicular linear axes, maintaining the leadangle or the trailing angle constant as a vector of movement of at leastone of the linear axis is changed.
 16. A method of programming atoolholder with a cutting tool, comprising the steps of: reversing adirection of rotation of a workpiece, and positioning the cutting toolon opposite side of a centerline of rotation of the workpiece, whereby aflank face of the cutting tool is utilized to perform a machiningoperation.
 17. A method of programming a machine tool comprising atleast three mutually perpendicular linear axes, one of a rotary axis anda rotation axis, and a toolholder mounted to a tool rest, the toolholderincluding a cutting tool, the method comprising the steps of providing amacro including a geometry of a workpiece to be machined and a geometricrelationship of the cutting tool with respect to the workpiece, wherebythe macro calculates the movement of the at least three mutuallyperpendicular linear axes, and the movement of one of the rotary axisand rotation axis about an axis other than a centerline of the workpiecethat is required to maintain a specified cutting tool geometry as thecutting tool proceeds across a surface of the workpiece.
 18. The methodaccording to claim 17, whereby the macro calculates a velocity of thecutting tool for each axis.
 19. The method according to claim 17,whereby the macro varies a distance between the cutting tool and theworkpiece such that a clearance angle of the cutting tool remainsconstant as the cutting tool moves toward a centerline of the workpiece.